Scrap and recycled copper metal is a plentiful and inexpensive form of copper. While some of this metal is simply smelted to form copper stock, another valuable use of this copper is the production of copper salts. Copper salts, of varying purity, are used as a supplement in animal feed, are used in fungicides, are used as pigments, and are used in a variety of other chemical processes.
It is known to produce copper hydroxide in a two-stage process from a previously produced copper salt, such as copper sulfate, copper carbonate or copper oxychloride, in a process in which alkali are added to effect a precipitation of copper hydroxide at a temperature below 20° C., as described in for example U.S. Pat. Nos. 3,635,668 and 4,490,337. There are also known methods of forming copper hydroxide directly from scrap metal. U.S. Pat. No. 2,536,096 discloses a single-stage process in which copper hydroxide is produced directly from scrap copper in a solution of ammonia in concentrations in excess of 10 g/l of soluble ammonium and preferably in excess of 30 g/l. U.S. Pat. No. 4,944,935 describes a process wherein copper metal is treated at a temperature of 0° to 40° with an aqueous solution which contains 0.1 to 10 g/l ammonium salt or ammonium hydroxide (calculated as NH3) with stirring and with a simultaneous introduction of an oxygen-containing gas, and the particulate copper (II) hydroxide reaction product is separated from the copper metal. This patent suggests using in the dissolution material 0 to 5 g/l copper (II) salt to make the reaction uniform.
Basic copper chloride (copper oxychloride) can be formed by treating copper carbonate with hydrochloric acid. The production of basic copper chloride via a reaction of copper metal and a chlorine source is known. Basic copper chloride may be manufactured either by the action of hydrochloric acid on copper metal or by the air oxidation of cuprous chloride suspensions.
However, to make other basic copper salts, heretofore the method of production has been to mix a first soluble copper salt with a second salt, under conditions where the copper ions from the first salt and the anions from the second salt form a precipitate. This is extremely inefficient. First, the copper metal must be converted into a soluble salt, which is typically copper chloride, copper nitrate, or copper sulfate. Second, the mixture of the two salts in water results in a large amount of waste brine (with residual copper) which must be treated prior to disposal. Third, the resulting copper salt invariably has a large amount of contamination from the anions and/or cations present in the two salts.
Basic copper carbonate (Cu2(OH)2CO3) (hereafter “BCC”) is used in a variety of applications, for example in pigments, pyrotechnics, insecticides, fungicides, astringents, and even as a feed additive. The traditional route to producing BCC is by adding sodium carbonate to a solution of copper sulfate, followed by filtering, washing, and drying. There are two inefficiencies in this method. First, copper sulfate must be prepared from copper metal or from other sources, and second, the washing of the solution in an attempt to remove the residual sulfates is expensive and produces a considerable amount of waste water requiring treatment before disposal. The formula for basic copper carbonate can be represented as CuCO3—Cu(OH)2, and while the theoretical amount of copper in basic copper carbonate is 57.48%, under manufacturing methods used today 56.0% is as high as conventionally practical. Generally, basic copper carbonate manufactured by this method has a high sodium content and a high sulfate content that can not be readily reduced by simple washing.
There are a number of other basic copper salts that are useful. Basic copper acetate is used as a pigment, insecticide, fungicide, mildew preventative, and as a mordant in dyeing. The chemical formula for basic copper acetate include blue verdigris, Cu(CH3COO)2.Cu(OH)2.and green verdigris, 2Cu(CH3COO)2.Cu(OH)2. Note that in formulas provided herein waters of hydration are typically not included. Basic copper sulfate (CuSO4-3Cu(OH)2) is also extensively used in industry, as a fungicide, and as a micronutrient for plants. Basic copper nitrate is also useful. Commercial preparation of these materials in each case requires the reaction of two dissolved salts to form the relatively insoluble product, and as a result there are costs associated with manufacturing the reactant salts and in removing contaminants.
What is needed is a method of directly forming a variety of basic copper salts from copper metal.